McGregor started with an early lead, coming out with energy and landing punches on Mayweather who failed to return any in the early bouts. But Mayweather prevailed in later rounds as McGregor, who was making his boxing debut, tired.

Referee Robert Byrd stopped the fight at 1:05 in the 10th round, deciding McGregor was unable to defend himself any further as Mayweather landed blow after blow.

"He's a lot better than I thought he was," Mayweather said of McGregor after the fight. "He's a tough competitor, but I was the better man tonight."

Mayweather said that tonight was his last time in the ring "for sure," after coming out of retirement twice before. It was a smashing end to a career that earned Mayweather more money than any fighter before him — including an estimated $200 million for his last bout.

McGregor said he disagreed with the Byrd's decision to end the fight, saying that he was tired but still willing to keep going if given the chance.

"He's not that fast, he's not that powerful but he's composed," McGregor said of Mayweather after the fight.

Though Byrd cautioned McGregor for hitting behind the head on two different occasions, there were no real fouls in the fight and McGregor never tried to revert to any MMA tactics.

McGregor had vowed to knock Mayweather out within two rounds, and he won the early rounds with movement and punches to the head. But the tide of the fight turned in the fourth round as Mayweather seemed to figure out what he had to do and began aggressively stalking McGregor.

Mayweather was credited with landing more than half his punches, as he solved McGregor's defense after a few rounds. Ringside stats showed him landing 170 of 320 punches to 111 of 430 for McGregor.

In a fight so intriguing that it cost $10,000 for ringside seats, McGregor turned in a respectable performance for someone in his first fight. But Mayweather's experience and his ring savvy paid off as he executed his game plan to perfection.

Some 50 million people in the U.S. alone were expected to gather with friends and family to see it all unfold.

Irish fans arrived by the thousands in the days before the fight, filling the arena for the weigh-in and boisterously cheering for their man. They even went off in the middle of the night and spray painted an Irish flag and "49-1" on a billboard on Interstate 15 promoting Mayweather's businesses.